There are growing demands on miniaturization of semiconductor devices, and consequently also on increase in current density required for wirings. According to the International Technology Road Map for Semiconductors (2002), maximum wiring current density necessary for semiconductor devices will rise almost close to 2×106 (A/cm2) at around 2005 or thereafter, which cannot be achieved by the conventional Cu wirings or the like.
One candidate of wiring materials capable of solving this sort of problem can be exemplified by carbon nanotube. Maximum current density of wiring made of carbon nanotubes is at an order of magnitude of 109 (A/cm2), approximately 1,000 times as large as that of the Cu wirings. The electric resistance thereof is known to be observed as a quantized resistance of approximately 6 kΩ per a single carbon nanotube. Low resistance wirings can therefore be formed by increasing the number of carbon nanotubes.
The carbon nanotubes can be configured as semiconductors by controlling the chirality, and has therefore been investigated about their use as a channel of a-field effect transistor. In this sort of field effect transistor, it is generally believed that conductance per unit width is several times as large as an N-channel transistor formed in a Si substrate, and as large as approximately 10 times as large as a P-channel transistor.
As one conventional method of forming a wiring composed of carbon nanotubes, there has been known a method of growing carbon nanotubes by a thermal CVD process or a plasma CVD process, selectively from the surface of a metal catalyst such as cobalt, nickel, iron or the like.
For example, Japanese Laid-Open Patent Publication No. 2002-329723 describes a method of forming a via-plug using carbon nanotubes, by allowing the carbon nanotubes to grow on a pattern of a metal catalyst in the vertical direction by a CVD process. The publication also describes a method of forming horizontally-extending wirings, by allowing the carbon nanotubes to grow, while being applied with electric field in the horizontal direction.
Japanese Laid-Open Patent Publication No. 2002-118248 describes a method of forming wirings horizontally extending as explained below. First, a line pattern of metal catalyst is formed, and a vertical growth suppressive layer is then formed thereon. Next, an opening is formed by a single process in the vertical growth suppressive layer and the line pattern. Carbon nanotubes are then grown between the patterns opposed in the opening. A description is made also on another method, in which a vertical growth suppressive layer is selectively formed, the line pattern is patterned, and the carbon nanotubes are grown thereafter.
Wolfgang Hoenlein (Jpn. J. Appl. Phys., Vol. 41 (2002) pp. 4370-4374) illustrates a carbon nanotube wiring applied by a damascene process, but no description is given on a method of forming the wiring.
It is, however, difficult to control the growth direction and the length of the carbon nanotubes in the method disclosed in Japanese Laid-Open Patent Publication No. 2002-329723. The method described in Japanese Laid-Open Patent Publication No. 2002-118248 is in need of forming the opening by a single process in the vertical growth suppressive layer and the line pattern of metal catalyst. It is, however, difficult to etch the metal catalyst such as Co, Ni, iron and the like, and the vertical growth suppressive layer in a series of process. In particular, the difficulty grows to a considerable degree, when the metal catalyst is thick. Moreover, any attempt of etching the metal catalyst by dry etching may cause adhesion of by-products on the side wall of the opening, from where the carbon nanotubes may undesirably grow. The method of selectively forming the vertical growth suppressive layer suffers from difficulty in controlling the direction of growth of the carbon nanotubes.
In the above-described literatures, there are no descriptions about methods of growing carbon nanotubes. It is also anticipated that the structure, having the metal catalyst selectively formed in a part of individual contacts, will be complicated.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2002-329723
[Patent Document 2] Japanese Laid-Open Patent Publication No. 2002-118248
[Non-Patent Document 1] Wolfgang Hoenlein (Jpn. J. Appl. Phys., Vol. 41 (2002), pp. 4370-4374)